JPH0115542B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recording liquid, and particularly to a recording liquid for so-called inkjet recording, which performs recording by being ejected from an ejection orifice of a recording head and flying as droplets. More specifically, the present invention relates to a recording liquid in which pigments are dispersed using a polymeric dispersant.

Among the various recording methods currently known, it is a non-impact recording method that generates almost no noise during recording, is capable of high-speed recording, and can record on plain paper without the need for special fixing processing. The so-called inkjet recording method is recognized as an extremely useful recording method. Regarding inkjet recording methods, various methods have been proposed so far, some have been improved and commercialized, and efforts are still being made to put them into practical use. .

This inkjet recording method is a method in which small droplets of a recording liquid called ink are ejected using various principles of operation, and the droplets are attached to a recording material such as paper to perform recording.

The ink used for this purpose is basically composed of a dye and its solvent, and the physical properties of the ink largely depend on the inherent properties of the dye. Therefore, when inkjet recording is conventionally performed using ink containing mainly water-soluble dyes, the resulting ink images are affected by the physical properties of the water-soluble dyes, and their water resistance and light resistance vary. It had the disadvantage of being inferior. Furthermore, the storage stability of ink itself containing such water-soluble dyes is not particularly high. Therefore, recently, attempts have been made to apply pigment-based inks to inkjet recording systems instead of such dye-based inks. This pigment-based ink has the advantage that the light fastness and water resistance of the obtained ink image are extremely good compared to images made using the dye-based ink. However, since the pigment is insoluble in the ink medium, a sophisticated technique is required to finely disperse it in the ink, and it is extremely difficult to improve its dispersion stability.

Nevertheless, the inkjet recording method requires the ink to be used to have liquid physical properties (viscosity, , surface tension, electrical conductivity, etc.), be stable for long-term storage and not cause clogging of the ink jet device,
Fast and reliable fixation on film (film, etc.), smooth dot periphery with little bleeding, clear color tone and high density of the formed ink image, and water resistance of the formed ink image.・
Various properties such as excellent light resistance, non-corrosion of materials surrounding the ink (container, connecting tube, sealing material), low odor and toxicity, and excellent safety such as flammability. It is required to have the following. However, it is quite difficult to simultaneously satisfy the above characteristics. The prior art described above is still unsatisfactory in this respect.

The present invention eliminates the drawbacks of the prior art described above and satisfies ejection stability, long-term storage stability, fixing performance, image density, clarity, water resistance, and light resistance at the same time, and is odorless, toxic, and flammable. The object of the present invention is to provide an inkjet recording liquid that uses a highly practical ink that is excellent in safety and other properties. Furthermore, it is an object of the present invention to provide a recording liquid that has excellent drive frequency response and is suitable for high-speed recording.

Accordingly, in the recording liquid of the present invention, fine pigment particles are dispersed in an aqueous dispersion medium containing a polymer having both a hydrophilic structural part and a hydrophobic structural part and a water-soluble organic solvent. In the recording liquid, the average molecular weight of the polymer is in the range of 1,000 to 100,000, and the ratio of the molecular weight of the pigment to the average molecular weight of the polymer is in the range of 1:2 to 1:150. There is.

Here, the pigment-based ink of the present invention will be explained in detail.

Pigment particles do not dissolve in solvents such as water, so even if they are simply mixed and dispersed in an ink solvent, they will immediately coagulate or settle and separate from the solvent, making it difficult to compose a practical ink. Can not. Therefore, when preparing such pigment-based ink,
A good dispersion medium for pigment particles is required.

Therefore, there is a method in which a polymer (dispersant) having both a hydrophilic structural part and a hydrophobic structural part is used as the first component of such a dispersion medium, and an aqueous liquid is used as the second component. This dispersion medium is about 1
The pigment particles can be dispersed very stably in the viscosity range of ~20 cps.

The polymer used as the first component of the dispersion medium is a polymer dispersant having a molecular weight of 1,000 to 100,000.
Examples of preferable polymeric dispersants include polyacrylic acid, polymethacrylic acid, condensed naphthalene sulfonic acid, and styrene, all of which have the above molecular weight range.
Maleic acid copolymer, diisobutylene-maleic acid copolymer, styrene-(meth)acrylic acid, (meth)acrylic acid ester-(meth)acrylic acid copolymer, styrene-itaconic acid copolymer, itaconic acid ester - itaconic acid copolymers, vinylnaphthalene-maleic acid copolymers, vinylnaphthalene-(meth)acrylic acid copolymers, vinylnaphthalene-itaconic acid copolymers, etc., and derivatives thereof.

In addition to the above polymers, for example, acrylonitrile,
Monomers such as vinyl acetate, (meth)acrylamide, N-methylol (meth)acrylamide, vinyl chloride, vinylidene chloride, ethylene, hydroxyethyl acrylate, glycidyl methacrylate, and hydroxypropyl methacrylate may be copolymerized. Some of these polymeric dispersants are commercially available and can be easily synthesized by known polymerization methods. Incidentally, it is necessary to form a salt of the polymer in order to solubilize or colloidally disperse the polymer in the aqueous liquid that is the second component. In addition to the alkali metals Na and K, mono-,
G or Tory (methyl aluminum), Mono, G,
or aliphatic amines such as Tory, (ethyl aluminum),
mono, g, or tri (ethanolamine),
Examples include alcohol amines such as mono, di, or tri (propanolamine), methylethanolamine, dimethylethanolamine, morpholine, N-methylmorpholine, and the like.

In the above polymer, the ratio of monomer units forming hydrophilic structural parts is particularly important. In other words, when the weight ratio of monomer units forming hydrophilic structural moieties such as carboxyl groups, sulfonic acid groups, or sulfuric acid ester groups exceeds approximately 40% by weight, the adsorption of the polymer to pigment particles decreases. Deteriorates the dispersion stability of pigment particles. On the other hand, when the amount is less than 2% by weight, the solubility of the polymer itself in the aqueous liquid decreases, and the polymer coagulates or precipitates in the aqueous liquid together with the pigment particles. Therefore, a more preferable ratio of the hydrophilic structural portion in the above polymer is considered to be about 25 to 40% by weight. Also, if the molecular weight of this polymer is too low, it will not contribute to the dispersion stability of the pigment particles, and conversely, if the molecular weight is too high, it will increase the viscosity of the ink itself too much (for example, 20 cps).
(above). Therefore, the molecular weight range of this polymer is preferably about 1,000 to 100,000.

Here, as a result of various experiments, the present inventor found that the ratio of the molecular weight W ₁ of the pigment to the average molecular weight W ₂ of the polymer
It has been found that there is a close relationship between W ₁ /W ₂ and the stability and driving frequency response of the dispersion. In other words, we prepared and investigated various dispersions with different molecular weights of pigment and polymer, and found that when the above ratio W ₁ /W ₂ was in the range of approximately 1/2 to 1/150. It was revealed that the stability of the dispersion liquid and the driving frequency responsiveness during ejection are good, and that the driving frequency responsiveness tends to decrease as the dispersion deviates from this, and the present invention has been completed.

In the ink used in the present invention, the amount of the polymer used is approximately 5 to 300 parts by weight, more preferably approximately 10 to 150 parts by weight, per 100 parts by weight of the pigment. If the upper limit of this range is exceeded, there are disadvantages such as a decrease in the color density of the ink and an inability to maintain the viscosity of the ink at an appropriate value. Moreover, when it is less than the following lower limit, the dispersion stability of pigment particles becomes poor.

The aqueous liquid components constituting the recording liquid of the present invention include water and water-soluble organic solvents. Examples of water-soluble organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-
Propyl alcohol, n-butyl alcohol,
Alcohols such as sec-butyl alcohol, tert-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; Ketone or keto alcohols such as acetone, methyl ethyl ketone, and diacetone alcohol; monoethanolamine, diethanolamine, and triethanolamine; Alkanolamines such as ethanolamine; amides such as dimethylformamide and dimethylacetamide; ethers such as tetrahydrofuran and dioxane; esters such as ethyl acetate, methyl benzoate, ethyl lactate, ethylene carbonate and propylene carbonate, ethylene glycol and diethylene glycol , triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerin, 1,2,6-hexanetriol, polyhydric alcohols such as thiodiglycol; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or Lower alkyl mono- or diethers derived from alkylene glycols such as ethyl) ether, propylene glycol monomethyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, diethylene glycol dimethyl (or ethyl) ether; pyrrolidone, N-
Methyl-2-pyrrolidone, 1,3-dimethyl-2
Examples include nitrogen-containing cyclic compounds such as -imidazolidinone and morpholine.

Among these many solvents, polyhydric alcohols or alkyl ethers of polyhydric alcohols, more preferably polyhydric alcohols such as diethylene glycol, are preferred in order to improve various properties required for recording liquids. Examples include alcohol. The content of these components is based on the total weight of the recording liquid.
In weight percent, generally 10 to 70%, preferably in order to reduce the temperature dependence of physical properties.
It is said to be in the range of 20-50%.

Further, the content of water at this time should be in the range of 5 to 90%, more preferably 10 to 70%, and still more preferably 20 to 70%, based on the total weight of the recording liquid. is desirable.

By the way, all kinds of organic pigments including conventionally known pigments can be used as pigments for composing the recording liquid of the present invention. For example, azo series, phthalocyanine series, quinacridone series, anthraquinone series,
Dioxazine series, indigo series, thioindigo series,
Examples include perinone-based, isoindorenone-based, and perylene-based pigments. These pigments are
The particle size in the recording liquid is in the form of fine particles of about several hundred millimeters to several microns, and preferably, it is suitable for use as an aqueous paste immediately after production.
The preferred concentration of this pigment in the recording liquid is approximately 3 to 30% by weight based on the total weight of the recording liquid, taking into account its influence on the coloring power and viscosity of the recording liquid.

In addition to the above-mentioned essential components, the recording liquid of the present invention may contain various conventionally known additives such as surfactants, salts, synthetic and natural resins, and various dyes.

The recording liquid of the present invention is composed mainly of the above-mentioned components, and various methods can be employed for its preparation. For example, a method is adopted in which the above-mentioned components are blended and mixed and ground using a ball mill, roll mill, speed line mill, homomixer, sand grinder, or the like.

The pigment dispersion process is carried out in a state where the pigment is as highly concentrated as possible, and after the dispersion treatment, this is diluted with an aqueous liquid, so that the final viscosity of the ink is about 1 to 15 cps, preferably about Adjusted to 2-10cps.

In the recording liquid prepared in this manner, pigment particles do not aggregate or settle even when stored for a long period of time in a low viscosity range.

This recording liquid has (1) liquid physical properties (viscosity, surface tension, electrical conductivity, It has excellent responsiveness particularly to high drive frequencies.

(2) Stable for long-term storage and does not cause clogging of the inkjet device.

(3) Fixation is fast and reliable on the recording material (paper, film, etc.), and the dot periphery is smooth and does not bleed.

(4) The color tone of the formed image is clear and the density is high.

(5) The formed image has excellent water resistance and light resistance.

(6) Do not damage materials surrounding the recording liquid (container, connecting tube, sealing material, etc.).

(7) It has various characteristics such as low odor, low toxicity, and excellent safety such as flammability.

Here, the present invention will be explained in further detail by showing examples.

Example 1 Styrene-maleate copolymer (molecular weight approx.
1500, trade name SMA resin 1440H, manufactured by Alco Chemical) 6 parts, triethanolamine 2 parts, water 60
part, 25 parts of ethylene glycol, and 7 parts of phthalocyanine blue (molecular weight 560), and milled with a ball mill to 48 parts.
A pigment dispersion was obtained by time dispersion (ratio of the molecular weight of the pigment to the average molecular weight of the polymer, W ₁ /W ₂ = 1/2.7). Coarse particles that could not be dispersed were removed using an ultracentrifuge to obtain a recording liquid for inkjet. Using this recording liquid, an on-demand recording head (discharge orifice diameter
50μ piezo vibrator drive voltage 60V, frequency 20KHz)
We investigated the printing characteristics using a recording device with

In addition, an on-demand type multi-head (discharge orifice diameter 35μ,
Heat generating resistor resistance value 150Ω, drive voltage 30V, frequency
The same study as above was conducted using a recording device with 5KHz).

In all cases, the recorded images obtained had excellent light fastness and water resistance, clear color tone and high density, smooth dot periphery without bleeding or blurring, and good fixing properties. In addition, the recording liquid does not cause aggregation or sedimentation of pigment particles even after long-term storage.
Stable discharge was achieved.

Example 2 10 parts of morpholine, 17 parts of diethylene glycol, 60 parts of water, and 7 parts of anthantrone orange (molecular weight 456) were added to 6 parts of diisobutylene-maleate copolymer (molecular weight approximately 10,000), and dispersed in a ball mill for 48 hours. A dispersion liquid was obtained (W ₁ /W ₂ =1/22).
After removing the coarse particles, the same study as in Example 1 was carried out, and as in Example 1, excellent results were obtained.

Example 3 Condensed naphthalene sulfonate (molecular weight approximately 1200,
Product name: Demol N (manufactured by Kao Atlas Co., Ltd.) 5 parts, 1 part of ethanolamine, 20 parts of glycerin, 74 parts of water,
Added 5 parts of Balarets (molecular weight 265) and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ =
1/4.5). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Example 4 Ammonium polyacrylate (molecular weight approximately 2000)
10 parts diethylene glycol monoethyl ether
20 parts of water, 64 parts of water, and 6 parts of Bordeaux 5B (molecular weight 270) were added and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ = 1/7.4). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Example 5 5 parts of ethyl acrylate-acrylic acid copolymer (molecular weight approximately 5000), 40 parts of water, and ethylene glycol
45 parts and 10 parts of Pyrazolone Red B (molecular weight 738) were added and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ =1/6.8). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Example 6 Styrene-octyl acrylate-itaconic acid monoethyl ester copolymer (molecular weight approximately 8000) 5
1 part of triethanolamine, 59 parts of water, 25 parts of diethylene glycol monoethyl ether, and 10 parts of benzidine yellow G (molecular weight 720) were added to the mixture and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ =
1/11). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Here, the present invention will be further explained in detail by showing synthesis examples and examples of polymers (dispersants).

Dispersant synthesis example (parts are parts by weight) Example 1 50% water in a four-necked separable flask equipped with a stirrer
1 part, 30 parts of isopropyl alcohol, 0.5 part of sodium dodecylbenzenesulfonate, and 0.5 part of ammonium persulfate are mixed and heated to 60°C. Separately, a mixed solution of 5 parts of styrene, 9 parts of acrylic acid, and 5 parts of butyl acrylate was placed in a separating funnel and gradually added dropwise over 60 minutes. After dropping, raise the temperature to 80°C and add 2 more times.
Polymerization was carried out by stirring for hours. The molecular weight of the obtained polymer was approximately 50,000.

Example 2 In a flask similar to Example 1, 8 parts of methyl methacrylate, 5 parts of styrene, 15 parts of itaconic acid, 1 part of benzoyl peroxide, 1 part of lauryl mercabutane, 50 parts of diacetone alcohol, and 20 parts of ethylene glycol were charged, and nitrogen gas was added. Polymerization was carried out for 6 hours while passing through the solution. The molecular weight of the obtained polymer was approximately 30,000.

A polymer was obtained from the following raw materials in the same manner as in Example 2.

Example 3 Styrene acrylonitrile methacrylate hydroxyethyl methacrylate azopisisobutyronitrile ethylene glycol monomethyl ether butanol 10 parts 5 10 5 1 19 50 (molecular weight: approximately 15,000) Example 4 Vinylnaphthalene dimethylamino Methacrylate Maleic anhydride Methyl ethyl ketone peroxide Isopropyl alcohol Triethanolamine 10 parts 5〃 10〃 1〃 60〃 14〃 (Molecular weight: approx. 20,000) Example 5 Styrene Maleic anhydride Diethanolamine Azobisisobutyronitrile Ethyl acrylate Ethyl carbitol Ethylene glycol monomethyl ether 10 parts 10 2 1 5 23 50 (Molecular weight: approx. 30,000) Example 6 Styrene itaconate monoethyl ester methacrylic acid 2-ethylhexyl methacrylate benzoyl peroxide n-propyl alcohol Ethylene glycol 5 parts 5〃 10〃 10〃 1〃 48〃 20〃 (Molecular weight: Approximately 80,000) Example 7 To 20 parts of the polymerization solution obtained in Synthesis Example 1, add 1 part of dimethylaminoethanol, 50 parts of water, and 20 parts of ethylene glycol.
and 5 parts of phthalocyanine blue (molecular weight 560) were added and dispersed in a ball mill for 48 hours to obtain a pigment dispersion (ratio of pigment molecular weight to polymer average molecular weight).
W ₁ /W ₂ = 1/89). Coarse particles that could not be dispersed were removed using an ultracentrifuge to obtain a recording liquid for inkjet. Using a recording device having an on-demand recording head (discharge orifice diameter 50μ, piezoelectric vibrator drive voltage 60V, frequency 4KHz) that discharges the recording liquid using a piezoelectric vibrator,
We investigated the printing characteristics.

In addition, an on-demand type multi-head (discharge orifice diameter 35μ,
Heat generating resistor resistance value 150Ω, drive voltage 30V, frequency
The same study as above was conducted using a recording device with 2KHz).

In all cases, the recorded images obtained had excellent light fastness and water resistance, clear color tone and high density, smooth dot periphery without bleeding or blurring, and good fixing properties. Further, even when the recording liquid was stored for a long period of time, the pigment particles did not aggregate or settle, and stable discharge was possible.

Example 8 1 part of morpholine was added to 20 parts of the polymerization solution obtained in Synthesis Example 2,
60 parts water, anthoanthrone orange (molecular weight 456)
7 parts were added and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ =1/66). After removing coarse molecules,
When we conducted a study in the same manner as in Example 1, we found that
Excellent results similar to those of Example 1 were obtained.

Example 9 1 part of ethanolamine, 25 parts of water, and 5 parts of Balaret (molecular weight 265) were added to 25 parts of the polymerization solution obtained in Synthesis Example 3, and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ = 1/57). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Example 10 To 20 parts of the polymerization solution obtained in Synthesis Example 4, add 10 parts of diethylene glycol monoethyl ether, 40 parts of water, and Bordeaux.
6 parts of 5B (molecular weight 270) was added and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ =1/74). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Example 11 15 parts of the polymerization solution obtained in Synthesis Example 6, 1 part of triethanolamine, 45 parts of water, 15 parts of ethylene glycol monoethyl ether, and benzidine yellow G (molecular weight
720) was added and dispersed in a ball mill for 48 hours to obtain a dispersion (W ₁ /W ₂ = 1/111). After removing the coarse particles, the same study as in Example 1 was conducted, and the same excellent results as in Example 1 were obtained.

Claims (1)

[Claims] 1 In a recording liquid formed by dispersing pigment fine particles in an aqueous dispersion medium containing a polymer having both a hydrophilic structural part and a hydrophobic structural part and a water-soluble organic solvent, the average molecular weight of the polymer is 1,000 to 100,000. and a ratio of the molecular weight of the pigment to the average molecular weight of the polymer is in the range of 1:2 to 1:150.